Synaptic activity depends on constant cycles of protein complex formation and dissociation, from the SNARE complexes that induce synaptic vesicle fusion to the clathrin:clathrin and clathrin:adaptor interactions required for endocytic retrieval of SV proteins. Regulating the assembly and disassembly of these complexes is the job of molecular chaperones, particularly the Hsp70s and their co-chaperone regulators. Chaperone dysfunction results in aggregation of the highly interactive proteins that form these complexes, and leads to neuronal dysfunction and neurodegeneration, induced either by aggregation-driven depletion of essential proteins or the toxic effects of the aggregates themselves. An understanding of chaperone mechanisms is therefore essential to understanding basic synaptic mechanisms and to understanding and treating neurodegenerative disease. Chaperones also have multiple functions in all cell types, and this adds to the significance of elucidating their mechanisms. Over the previous project period our focus on the roles and mechanisms of molecular chaperones in synaptic function has increased. We now propose to pursue the following broad themes: (1) Characterization of the structures, mechanisms, and regulation of two chaperones--Hsp110 and Hip--that have been relatively understudied, but that are highly abundant in brain and that have demonstrated roles in neuronal function or neurodegenerative disease. (2) Elucidation of the role of chaperone:chaperone associations in chaperone function and inhibition of neurodegenerative disease. This work is expected to advance our fundamental understanding of the mechanisms that underlie synaptic transmission, and as such will be a critical part of our efforts to fight neurological disorders.